The present invention relates to voltage regulators for photovoltaic charging systems and in particular to a sequential switching regulator for selectively shedding and reinserting portions of a photovoltaic array into a storage battery charging system.
Solar photovoltaic systems are conventionally arranged to supply charging (or recharging) power to storage batteries, such as rechargeable lead-acid or nickel cadmium battery systems. As a conventional battery is recharged, the terminal voltage of the battery gradually rises. The terminal voltage continues to rise corresponding to the amount of energy supplied to the battery. Even after the storage battery has reached full charge, the terminal voltage may continue to rise until the voltage reaches the gassing potential (lead-acid battery) of the electrolyte. If a charging voltage above the gassing potential is maintained, the storage battery will lose its electrolyte deteriorating battery output, and possibly destroying the storage battery. This situation is typically avoided by interposing a voltage regulator between the photovoltaic array and the storage battery. When the storage battery is fully charged, the regulator serves to shunt charging power from the battery. The regulator normally shunts the array's entire charging capability, which requires that the regulator's power dissipating device(s) handle the entire array electrical load. To overcome these and other disadvantages of existing regulators, the regulator circuit of the present invention monitors the terminal voltage of the storage battery, and, when necessary, sheds or reinserts portions of the photovoltaic array to the charging system.